This paper presents a robust numerical model for dealing with temporary instabilities which occur in the numerical analysis of steel structures under fire conditions. The model adopts the combined static-dynamic solution procedure to model ‘snap-through’ behaviour of industrial steel portal frame in fire. This new method allows solution procedure automatically switch between static and dynamic approaches, with the objective mainly for overcoming a transitory stage of instability in structural modelling. The current model is computationally very efficient compared to conducting full dynamic analysis of the structures for the whole duration of fire. The method could easily be applied for modelling composite and reinforced concrete buildings under fire conditions. The snap-through instability of the pitched portal frame has been modelled successfully by the new procedure. The method could provide a very useful modelling tool for the perform-based fire safety design of industrial buildings, as a much more realistic alternative to the highly simplified design methods which are currently in use.
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